It is known in this field to make paper sheets consisting of several creped plies exhibiting a specific surface weight between 12 and 30-35 g/m2 and fitted with protrusions made by embossing.
Embossing imparts bulk to the sheet and improves touch, softness and liquid absorption. Attempts already have been made to further improve absorptivity by means of multi-ply sheets made by linking at least two plies, each consisting of at least one of the embossed foils.
In this manner a sheet of several plies is attained which offers specific mechanical features, such as tensile strength and absorptivity.
Presently there are two embossing and ply-joining modes depending on the desired properties of the end product.
The first mode relates to “nesting”. It consists in first embossing each ply separately so as to form at the surface generally substantially frustoconical or frusto-pyramidal protrusions. Next, an adhesive is deposited on the top of the protrusions of one of the plies following its embossing but before it is detached from the embossing cylinder. The plies are mutually lined up in such a way that the protrusions of one ply face the protrusions of the other and that these protrusions of one side and the other shall nest between one another. Finally they are assembled by moving them close together. Accordingly, the two plies are connected by films of adhesive at the protrusion tops of one ply and unembossed zones which are situated between the protrusions of the other ply. The cavities subtended in this structure reliably assure improved absorption. Furthermore, the outer sides offer a smooth and velvety touch on account of the alveoles constituted by the backs of the protrusions. This technique is illustrated in U.S. Pat. No. 3,867,225.
The second joining mode is known in the field as “tip-to-tip”. It differs from the preceding mode by the relative configuration of the two plies. After these were separately embossed, they are moved one on the other in a way to make the tips of the protrusions coincide in part or in whole. The plies are connected to each other by the tip-to-tip arrayed protrusions. This technique is illustrated in U.S. Pat. No. 3,414,459.
The products manufactured by the above techniques have long exhibited a plain embossing pattern wherein the protrusions were uniformly arrayed in two crossing directions. While such a pattern allows attaining homogeneous properties, its visual attractiveness is modest.
For several years already attempts have been made to enhance product appearance by spreading the protrusions in different ways. Applicant; for example, is marketing a paper towel of which the surface alveoles are arrayed in concentric circles suggesting the propagation of a liquid which was poured on an absorbent sheet being absorbed, or also surface wave propagation when a drop of water falls on a liquid. More specifically, such a pattern can consist of distinct first disk-shaped zones defined by three or four concentric circles. The disks in turn are regularly configured along crossing directions. Second zones defined between adjacent disks generally assume a diamond shape.
Provided such a pattern is visually perceptible to the user, it will be commercially significant.